1. Field of the Invention
The present invention relates to a crystal element and a crystal device that is provided with the crystal element. The crystal device is a crystal vibrator or a crystal oscillator, for example.
2. Description of the Related Art
The crystal element is configured with a crystal piece that is a mesa type and in a substantially rectangular shape in a plan view and a metal pattern provided on the crystal piece, for example. The metal pattern is configured with a pair of excitation electrodes, a pair of leading sections, and a pair of wiring sections. The pair of excitation electrodes is provided on both main surfaces of the crystal piece. The pair of leading sections is for mounting the crystal element to an element loading member, and disposed in opposition to a loading pad of the element loading member. One end of the pair of wiring sections is connected to the excitation electrodes, and the other end thereof is connected to the leading sections. Through electrically connecting the leading section and the loading pad of the element loading member via a conductive adhesive, the crystal element is supported like a cantilever beam and mounted to the element loading member.
The crystal piece used for such crystal element includes, for example, an oscillation section containing a pair of protrusions projected to mutually opposing directions, and a peripheral section that is thinner than the thickness of the oscillation section and provided along an outer edge of the oscillation section. In this case, the long side of the crystal piece is in parallel to the X-axis that is one of the crystalline axes of the crystal piece. Meanwhile, the short side of the crystal piece is in parallel to the Z′-axis that is rotated from the Z-axis that is one of the crystalline axes of the crystal piece. One of the protrusions includes a side face sloping with respect to the main surface of the protrusion itself and a side face perpendicular to the main surface of the protrusion itself in a sectional view taken along the thickness direction of the crystal piece facing in the direction in parallel to the Z′-axis. The other protrusion includes a side face sloping with respect to the main surface of the other protrusion itself and a side face sloping with respect to the main surface of the other protrusion itself in a sectional view taken along the thickness direction of the crystal piece facing in the direction in parallel to the Z′-axis. In a plan view taken along the thickness direction, the crystal pieces are disposed in such a manner that the side face sloping with respect to the main surface of one of the protrusions overlap with the side face perpendicular to the main surface of the other protrusion while the side face perpendicular to the main surface of one of the protrusions overlaps with the side face perpendicular to the main surface of the other protrusion (e.g., see Japanese Unexamined Patent Publication No. 2013-197621 (Patent Document 1)).
Such crystal element is so structured that a part of the crystal piece sandwiched between the pair of excitation electrodes oscillates when an alternate voltage is applied to the metal pattern. In that case, the oscillation of the crystal piece sandwiched between the pair of excitation electrodes propagates from the outer edge of the excitation electrodes toward the outer edge of the crystal pieces in a plan view, i.e., in the direction toward the side face of the protrusion. When the oscillation propagates to the outer edge of the crystal piece, specifically to the side face of the protrusion, the oscillation is reflected at the side face of the protrusion. The conventional crystal element uses the crystal piece that includes the protrusion having the side face perpendicular to the main surface of the protrusion itself and the other protrusion having the side face perpendicular to the main surface of the other protrusion itself, and the excitation electrodes are provided on the both main surfaces of the crystal piece, i.e., on the main surface of the protrusion and the main surface of the other protrusion. Thus, the reflection amount of the oscillation propagated from a part of the crystal piece sandwiched between the pair of excitation electrodes becomes greater in the side face that is perpendicular to the main surface of the protrusion compared to that of the side face sloping with respect to the main surface of the protrusion. Therefore, the oscillation of a part of the crystal piece sandwiched between the excitation electrodes and the reflected oscillation are combined. As a result, the equivalent series resistance value becomes increased so that the electric characteristic may be deteriorated.
It is an exemplary object of the present invention to provide a crystal element and a crystal device capable of decreasing changes in the electric characteristics caused when the oscillation propagated from a part of the crystal piece sandwiched between the excitation electrodes is reflected at the side face of the protrusion.